Hydroxy Acids: What They Do and Which Ones Are Right for You

BY Tracy O’Connor · September 11, 2017

At this stage, most of us have used a product or two that contains hydroxy acids. Glycolic, lactic, salicylic—we’ve heard of them. We know they work, but what exactly does each of them do? How are they different from each other? And, most importantly, which ones do what best? Let us break it down for you.

How Hydroxy Acids Work

“Hydroxy acids can do a lot of things,” says triple-board certified plastic surgeon Stanley Jacobs. “They smooth, tighten, firm and brighten. And what’s great, almost everyone can tolerate them in lower concentrations and over-the-counter formulations and will notice significant improvements in their skin when used as directed.”

But how exactly do these multitaskers-in-a-bottle work? Beverly Hills-based, board-certified dermatologist Dr. Haleh Bakshandeh explains: “Hydroxy acids weaken the ‘cellular glue’ that makes dead skin cells stick together, encouraging exfoliation and revealing healthy, younger skin cells. Hydroxy acids at medium to higher concentrations can also function beyond the surface of the skin and work in the epidermal and dermal layers to deliver additional results, such as collagen and elastin remodeling, pigment lightening and melanin suppression (i.e., keeping brown spots at bay).”

How to Use Hydroxy Acids

While using hydroxy acids is common and generally safe for your skin, knowing when, how and in what amount can make your product much more effective and less likely to cause irritation. Here are the 5 commandments when using hydroxy acids for the first time.

1. Start Slow. In general, when using acids, always start conservatively with a lower concentration and then work up to see what your skin can tolerate.

2. Do a Patch Test. Apply a small amount on the arm and then on the forehead (where the facial skin is the thickest) to see how your skin will respond.

3. Use a Daily Sunscreen. Studies show that AHAs leave the skin sensitive to UV radiation while using the products and for weeks after discontinuing use.

4. Consult Your Doctor. It is not uncommon for people to experience mild redness and peeling when first beginning an AHA/BHA skin care regimen. If persistent irritation or redness occurs, consult a doctor.

The Hydroxy Acid Alphabet

Let’s start with the basics. Hydroxy acids fit into two categories: Alpha hydroxy acids (AHAs) and beta hydroxy acid (BHA). Both groups of acids are naturally derived from various foods (e.g., sour milk, sugarcane) and plant-based sources (e.g., willow bark). They also work similarly, but each one produces slightly varied results. The main difference? AHAs are water-soluble (dissolves in water) and BHA is lipid or oil-soluble, which makes BHA more effective on oily skin.

Though there are various types of acids, glycolic, lactic, mandelic, citric and salicylic acids have the most clinical research behind them and the most studies supporting their efficacy. That’s why they’re also the most commonly used acids in skin care products. Here’s what else you need to know about each of them:

1. SALICYLIC ACID

In a nutshell: Salicylic acid is a naturally occurring BHA derived from willow bark (the same place we get aspirin).

Why it works: According to Dr. Jacobs, salicylic acid is both highly keratolytic and comedolytic, which means it not only dissolves dead skin cells on the surface of the skin, but it’s also able to get down into the pore, dissolve the oil and break apart the debris inside that commonly leads to acne.

Who will benefit from it: Unlike glycolic acid, salicylic acid is oil-soluble and can penetrate, polish and clear inside the pore. When used regularly, salicylic acid not only unclogs pores and helps clear acne, but it also prevents new acne and blackheads from forming. Additionally, it can correct dark spots without irritating your skin because it’s derived from willow bark, which has some topical anti-inflammatory benefits. “While some AHAs and other acids can trigger post-inflammatory hyperpigmentation in patients with darker skin types, you won’t see that with salicylic acid,” Dr. Bakshandeh explains. “It’s a very safe and predictable acid. I use it to treat patients with darker skin looking to correct sun and age spots and hyperpigmentation issues.”

What else you need to know: It should be noted, that while salicylic acid is proven effective against some acne, it does have its limitations. While BHA has been shown to be mildly antibacterial, it has not been shown to kill p. acnes bacteria, the most common bacteria that leads to acne. For this reason, salicylic acid is often paired with antibacterial ingredients or benzoyl peroxide for the best results. Salicylic acid can also be mildly drying to the skin, so it’s important to moisturize when using it. Dermatologists recommend a salicylic acid formulation that contains 0.5% up to 2%.

2. GLYCOLIC ACID

In a nutshell: This naturally occurring sugarcane-derived AHA has long been considered by many professionals to be the best-performing AHA. As the smallest hydroxyl acid molecule, glycolic acid can penetrate the skin the deepest and the fastest.

Why it works: Like all AHAs, glycolic acid exfoliates the skin by dissolving the cellular glue and exfoliating superficial, dead skin cells. Because glycolic penetrates the deepest—and some studies suggest all the way into the dermis—it has been shown to be the most effective at stimulating collagen production, thus better promoting deeper wrinkle reduction.

Who will benefit from it: Aside from reducing wrinkles, glycolic acid is also effective at reducing photodamage, which makes it ideal for those with more mature skin. If you have dry skin, you’ll also find glycolic particularly useful, because it draws moisture to the skin and helps prevent transepidermal water loss. It also increases the hyaluronic acid levels in the skin.

What else you need to know: It’s important to know that because glycolic acid penetrates quickly, it can be more irritating than other AHAs and is sometimes not tolerated well by sensitive skin types.

3. LACTIC ACID

In a nutshell: Lactic acid is a naturally occurring acid derived from a variety of sources, most commonly sour milk. Cleopatra is believed to have bathed in it as part of her beauty rituals.

Why it works: Like glycolic acid, lactic acid exfoliates as it increases moisture levels in the top layers of the skin, improving barrier function and resistance to dryness and flakiness.

Who will benefit from it: Like all AHAs, lactic acid is great for general exfoliation and skin lightening. But because this is a larger molecule, it makes it somewhat “gentler” than glycolic acid. Dr. Bakshandeh explains: “Those with sensitive skin or darker skin often prefer lactic products over glycolic acid products because they tend to see less inflammation in the skin after use, but get similar desired results.”

What else you need to know: Studies show that low concentrations and medium (12%) concentrations of lactic acid can increase epidermal and dermal firmness and thickness of skin as well as reduce the appearance of lines and wrinkles. It can also clear sunspots by accelerating cell turnover and directly inhibiting melanin production.

4. MANDELIC ACID

In a nutshell: Mandelic acid is a naturally occurring acid derived from bitter almond and wild cherry.

Why it works: Mandelic acid is a highly effective, renaissance acid that works on a lot of things, including fine lines, firmness, acne and discoloration. And because mandelic is a slightly larger molecule, it’s better for sensitive skin types and for those with darker skin because it doesn’t trigger post-inflammatory responses or pigmentation like we see from other AHAs.

Who will benefit from it: Because of its antimicrobial properties, it’s effective against acne, both cystic and comedones. In fact, in a clinical study comparing a mandelic-salicylic acid combination peel with a glycolic peel, the combined mandelic-salicylic peel saw better overall results and had fewer side effects.

What else you need to know: According to Dr. Jacobs, in preliminary trials done using cutometer technology to measure skin elasticity, mandelic acid also proved effective at improving skin elasticity. He believes mandelic acid is going to be one of the next big ingredients in skin care.

5. CITRIC ACID

In a nutshell: It is a naturally occurring acid derived from fruits, including orange, lemon and grapefruit. It is often used in skin care formulations to provide natural fragrance and preservative properties.

Why it works: Citric acid is antimicrobial and often formulated into acne products for its bacteria-busting powers.

What else you need to know: Recent studies also showed patients using a 20% citric acid lotion saw an increase in dermal thickness. However, studies report citric acid is not as effective as glycolic or lactic in improving photodamage or dark spots.

Whatever your skin type, tone or condition, there is so much research behind hydroxy acids supporting their numerous benefits. Find which ones are right for you and you will likely find yourself with happier, healthier skin. Hello, glow!

Tracy O’Connor is a New York Times best-selling author, lifestyle reporter and sought after beauty industry consultant. She is a regular contributor to Fox Good Day LA and has a monthly column in Genlux Magazine. She ... Read More >